Polyanilines, synthesis emeraldine salt

The emeraldine salt of polyaniline which is one of the three different forms of polyaniline—leucoemeraldine (the fully reduced state], emeraldine (the half oxidized state] and pernigraniline (the fully oxidized state] (Fig. 8.1]—is electrically conductive while the others are insulators. Conventional chemical synthesis of polyaniline is based on an oxidative polymerization of aniline by using an oxidant in the presence of a strong acid dopant in the reaction mediunL ... 

Polyanilines (PAns) have been known for more than a century, since the synthesis of the so-called "aniline blacks" that enjoyed an early use as cotton dyes in the 1860s. Systematic studies of their properties prior to World War I led to the proposal by Green and Woodhead of an aniline octamer structure and the existence of several oxidation states. Only sporadic studies of polyanilines were undertaken over the following 70 years, until investigations by MacDiarmid et al. in the mid 1980s, and, in particular, the discovery of electrical conductivity for its emeraldine salt form, led to an explosion of interest in this fascinating polymer. 

Han et al. [64, 66] reported the synthesis of highly conductive and thermally stable self-doped mercaptopropanesulfonic-acid-substituted polyanilines by the concurrent reduction and substitution reaction between polyaniline and a nucleophile. These reactions were carried out on both electrochemically generated and free standing polyaniline films prepared from emeraldine base dissolved in N-methylpyrrolidinone. The electrochemically prepared films were dedoped with 5 % aqueous NaiCOs to convert them the into the emeraldine base form. The sulfonated polyaniline was prepared by reaction of a polyaniline emeraldine base film with 0.1 M 3-mercapto-l-propanesulfonic acid sodium salt in methanol under nitrogen at room temperature for approximately 14h [66]. A catalytic amount (0.01 M) of acetic acid was reported to accelerate the reaction. The resulting sulfonated polyaniline film was thoroughly rinsed with methanol, followed by 5 % aqueous NaiCOs to remove reactants. 

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